Summary: Fluctuations in the microwave conductivity of YBa2Cu3O7 single crystals
in zero dc magnetic field
Steven M. Anlage, J. Mao, J. C. Booth, Dong Ho Wu, and J. L. Peng
Center for Superconductivity Research, Department of Physics, University of Maryland, College Park, Maryland 20742-4111
Received 16 June 1995; revised manuscript received 5 October 1995
We present a quantitative analysis of finite frequency fluctuation conductivity above and below Tc in cuprate
superconductors in zero dc magnetic field. In a YBa2Cu3O7 crystal showing a linear in temperature increase
of the penetration depth at low temperatures, we find that two-dimensional 2D finite frequency Gaussian
conductivity fluctuations above Tc cross over into a slower divergence of the conductivity as Tc is approached
from above. We find that the critical regime above Tc is less than about 0.6 K wide. At and below Tc , 3D
fluctuations dominate the conductivity, with evidence of 3D XY critical scaling of the imaginary part of the
conductivity down to 5 K below Tc .
Cuprate superconductors differ from their low-
temperature counterparts in a number of significant and dra-
matic ways. Their small superconducting coherence length,
reduced dimensionality imposed by the CuO2 planes, low
carrier density and high transition temperature lead to situa-
tions where superconductivity can be strongly affected by the
large thermal energies available. The cuprates offer the op-
portunity to establish the nature and universality class of